U.S. Pat. No. 4,918,690 discloses a network for providing sensing, communications, and control. The disclosure of this patent is incorporated herein by reference. By way of brief summary, the network comprises a plurality of intelligent cells, each of which comprises an integrated circuit having a processor and input/output section. Each of the programmable cells receives a unique identification number which remains permanently within the cell. The cells can be coupled to any one of a variety of media such as power line, twisted pair, radio frequency, infrared, ultrasonic, optical, coaxial, etc. to form the network. Cells communicate with one another on the network by exchanging packets of data.
Each network may comprise groups of cells that perform particular functions. Cells can perform multiple functions and be members of multiple groups. The network protocol provides great flexibility and allows groups to be formed and/or changed after the cells are in place. The intelligence of the network is distributed among the cells. In general, the network is lightly loaded, although provisions may be made for contentions and other overload conditions that may arise. Communications between the cells in general is optimized for carrying out the functions assigned to the groups, rather than for transmission of data unrelated to the control function of the network. For this reason, communication packets are relatively short compared to more conventional local area networks.
A portion of a network of cells is illustrated in FIG. 1. Here, cells 20 and 30 are coupled to a communications medium 40 by means of respective transceivers 22 and 32. Additionally, each cell may be coupled to one or more of a variety of input/output devices 25, such as sensors and actuators, that interface with the environment and enable the cell to perform its assigned function in the network. For the purpose of the description to follow, the term "cell" will refer to the intelligent device coupled to the network, whereas a cell and its associated peripheral devices, including a transceiver and any input/output devices, will be referred to as a node.
As an example of a typical network application, cell 20 may be associated with a lighting fixture in a home, and cell 30 may be associated with a light switch. In this application, medium 40 may be the house wiring, although it could also be any of the other media recited above. Cell 30 would be assigned the function of sensing the opening or closing of its associated switch, while cell 20 would be assigned the function of controlling the flow of power to its associated light fixture in accordance with command and control information received over the network from cell 30 and from any other nodes that are functionally related, such as, for example, a node that senses ambient light levels.
Commercial embodiments of a device that may be employed as cells 20,30 are the integrated circuits sold under the trademark "NEURON" by both Motorola and Toshiba. These devices are manufactured under license from Echelon Systems Corp., the assignee of this invention and owner of the aforementioned U.S. Pat. No. 4,918,690. Briefly stated, a "NEURON" cell is a large scale integrated circuit device including a three-processor CPU, internal memory, communications port, I/O section and timing and control section. The three independent processors share a common memory, arithmetic logic unit (ALU) and control circuitry. Two of the processors are dedicated to communications and the third is dedicated to execution of application code.
Transceivers 22,32 are specifically designed for the particular network medium 40. Moreover, the transceivers may be simple line drivers in the case of a hardwired network medium or may be more sophisticated devices. Characteristics of a more sophisticated transceiver may include:
Multiple channel operation. PA1 Multiple speed PA1 Use of forward error correction. PA1 Media specific modulation techniques requiring special message headers and framing. PA1 Programmable and configurable operation. PA1 Ability to gather parametric data regarding transmission quality, noise, and received signal strength. PA1 Ability to shut down to save power during idle time. PA1 Definition of the registers that the cell may read and write. PA1 Definition of preamble. PA1 Use of watch dog timers on the transceiver (e.g., such that the node does not fail in a way that ties up the network indefinitely). PA1 Use of transceiver run/sleep modes.